Heat management systems for energy conversion devices oftentimes utilize fuels as cooling mediums, particularly on aircraft and other airborne systems where the use of ambient air as a heat sink results in significant performance penalties. In addition, the recovery of waste heat and its re-direction to the fuel stream to heat the fuel results in increased operating efficiency. One of the factors negatively affecting the usable cooling capacity of a particular fuel with regard to such a system is the rate of formation of undesirable oxidative reaction products and their deposit onto the surfaces of fuel system devices. The rate of formation of such products may be dependent at least in part on the amount of dissolved oxygen present within the fuel. The amount of dissolved oxygen present may be due to a variety of factors such as exposure of the fuel to air and more specifically the exposure of the fuel to air during fuel pumping operations. The presence of dissolved oxygen can result in the formation of hydroperoxides that, when heated, form free radicals that polymerize and form high molecular weight oxidative reaction products, which are typically insoluble in the fuel. Such products may be subsequently deposited within the fuel delivery and injection systems, as well as on the other surfaces, of the energy conversion device detrimentally affecting the performance and operation of the energy conversion device. Because the fuels used in energy conversion devices are typically hydrocarbon-based, the deposit comprises carbon and is generally referred to as “coke.”
Increasing the temperature of the fuel fed to the energy conversion device increases the rate of the oxidative reaction that occurs. Currently available fuels that have improved resistance to the formation of coke are generally more expensive or require additives. Fuel additives require additional hardware, on-board delivery systems, and costly supply infrastructure. Furthermore, such currently available fuels having improved resistance to the formation of coke are not always readily available.